(1) Field of the Invention
The present invention relates to a corona shield for tension insulator assemblies, and more particularly to a shield for preventing corona discharge occurring on the energized side of tension insulator assemblies mainly for extra-high and ultra-high voltage overhead transmission lines.
(2) Description of the Prior Art:
Recently, as the capacity of the electric power transmission has generally been greatly increased, the insulator assemblies for extra-high and ultra-high voltage overhead transmission lines have become large in size. In general, these insulator assemblies have attached ring horns integral therewith or separate therefrom for preventing corona discharge or protecting the insulators from arc. The shields for such large-sized insulator assemblies require correspondingly large-sized ring horns having large pipe diameters and outer diameters.
The hitherto used shielding with ring horns, however, has a disadvantage in that the corona characteristic of the shielding ring itself becomes degraded due to corona discharge from water droplets on the shielding ring under wet conditions, although a sufficient shielding effect can be expected under dry conditions.
To overcome this disadvantage, it has been suggested that metal tubes having small diameters be turned into the form of a cage to provide a shielding ring having a large outer diameter. However, a shielding ring of this type is not practical because it is difficult to install and expensive to manufacture and is likely to be covered with snow.